The present invention relates to an offshore installation for transferring a liquefied gas, especially liquefied natural gas, particularly from one tank to another tank via a submerged transfer line.
The present invention relates to an offshore installation for transferring a liquefied gas, especially liquefied natural gas, as described in the preamble of claim 1.
It applies especially to methods of filling transport ships with liquefied gas or liquefied natural gas (LNG tankers).
Methods of filling transport ships with natural gas and liquefied natural gas are known.
The known gas transport ships have tanks for transporting gas in the liquid state and, in certain cases (liquefied petroleum gas), they include a gas liquefaction installation.
To fill these ships with liquefied gas, the liquefaction installation is linked to a transfer line which is connected to a source of liquefied gas, for example an onshore or offshore storage tank.
Also known are methods of filling a ship with liquefied gas in which the gas is liquefied and stored in a temporary storage tank located, for example, on a production platform. The liquefied gas is then transferred onto the ship via a transfer installation.
Such a transfer installation is described in document FR-A-2 793 235. This transfer installation is composed of a plurality of articulated hose segments in the form of deformable lozenges, the ends of which are connected, on one side, to a connection system on the ship. and, on the other side, to a hose placed alongside a crane.
This installation has to meet significant mechanical constraints. It is placed near the production platform and must be able to adapt to the movements of the production platform (six degrees of freedom, including roll, pitch, heave, surge). In addition, the installation includes many rotary seals, which are in constant movement. Its maintenance is therefore relatively expensive. This type of installation is used for the loading and unloading of LNG tankers in ports of production terminals or those for receiving liquefied natural gas, alongside sheltered jetties.
Other liquefied gas transfer installations are known. These installations are used for transferring liquefied gas or liquefied natural gas (LNG) between two ships. Such installations mean that the two ships have to be positioned one behind the other or else side by side.
In both these configurations, the distance separating the ships is relatively small. The two ships have large and similar dimensions and are subjected to swell and to currents. Thus, each of them moves with six degrees of freedom and relatively independently of the other. The transfer installation is designed to take account of these relative movements of the two ships, which are also dependent on the weather conditions.
Another transfer installation, known for example from French Patent application FR-A-2 815 025, comprises a flexible transfer hose in a form of a catenary linking the storage installation to the transport ship. At rest, the flexible hose is stored on a gantry associated with a production and storage installation. The flexible hose is connected to the ship via a connection module fastened to or independent of this flexible hose.
Patent application WO 01/87703 proposes an installation for transfer from a production site to an LNG tanker. This installation is composed of an arm placed on the production site and extending over a length of 30 to 60% of the safety distance between the two ships. A flexible hose is wound onto a wheel at the end of the arm. This hose is connected to the LNG tanker during transfer.
Document WO 01/34460 proposes an overhead installation for transferring liquefied natural gas between two ships with a connection system mounted on the end of a flexible hose, which is connected to the installation of the second ship.
In all these known devices, the hoses used for transferring the gas have only a relatively short length (less than 100 meters) and lie above the surface of the sea. Consequently, the ship can be loaded only when it is close to the platform or the delivery ship, thereby creating risks of collision and making the transfer device very dependent on the weather conditions.